mirror of https://github.com/postgres/postgres
This patch creates an API whereby a btree index opclass can optionally provide non-SQL-callable support functions for sorting. In the initial patch, we only use this to provide a directly-callable comparator function, which can be invoked with a bit less overhead than the traditional SQL-callable comparator. While that should be of value in itself, the real reason for doing this is to provide a datatype-extensible framework for more aggressive optimizations, as in Peter Geoghegan's recent work. Robert Haas and Tom Lanepull/1/head
Tom Lane
14 years ago
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d2a662182e
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/*-------------------------------------------------------------------------
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* |
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* sortsupport.c |
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* Support routines for accelerated sorting. |
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* |
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* |
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* Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* IDENTIFICATION |
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* src/backend/utils/sort/sortsupport.c |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "fmgr.h" |
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#include "utils/lsyscache.h" |
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#include "utils/sortsupport.h" |
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/* Info needed to use an old-style comparison function as a sort comparator */ |
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typedef struct |
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{ |
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FunctionCallInfoData fcinfo; /* reusable callinfo structure */ |
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FmgrInfo flinfo; /* lookup data for comparison function */ |
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} SortShimExtra; |
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/*
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* sortsupport.h defines inline versions of these functions if allowed by the |
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* compiler; in which case the definitions below are skipped. |
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*/ |
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#ifndef USE_INLINE |
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/*
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* Apply a sort comparator function and return a 3-way comparison result. |
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* This takes care of handling reverse-sort and NULLs-ordering properly. |
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*/ |
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int |
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ApplySortComparator(Datum datum1, bool isNull1, |
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Datum datum2, bool isNull2, |
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SortSupport ssup) |
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{ |
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int compare; |
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if (isNull1) |
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{ |
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if (isNull2) |
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compare = 0; /* NULL "=" NULL */ |
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else if (ssup->ssup_nulls_first) |
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compare = -1; /* NULL "<" NOT_NULL */ |
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else |
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compare = 1; /* NULL ">" NOT_NULL */ |
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} |
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else if (isNull2) |
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{ |
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if (ssup->ssup_nulls_first) |
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compare = 1; /* NOT_NULL ">" NULL */ |
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else |
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compare = -1; /* NOT_NULL "<" NULL */ |
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} |
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else |
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{ |
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compare = (*ssup->comparator) (datum1, datum2, ssup); |
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if (ssup->ssup_reverse) |
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compare = -compare; |
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} |
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return compare; |
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} |
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#endif /* ! USE_INLINE */ |
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/*
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* Shim function for calling an old-style comparator |
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* |
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* This is essentially an inlined version of FunctionCall2Coll(), except |
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* we assume that the FunctionCallInfoData was already mostly set up by |
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* PrepareSortSupportComparisonShim. |
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*/ |
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static int |
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comparison_shim(Datum x, Datum y, SortSupport ssup) |
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{ |
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SortShimExtra *extra = (SortShimExtra *) ssup->ssup_extra; |
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Datum result; |
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extra->fcinfo.arg[0] = x; |
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extra->fcinfo.arg[1] = y; |
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/* just for paranoia's sake, we reset isnull each time */ |
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extra->fcinfo.isnull = false; |
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result = FunctionCallInvoke(&extra->fcinfo); |
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/* Check for null result, since caller is clearly not expecting one */ |
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if (extra->fcinfo.isnull) |
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elog(ERROR, "function %u returned NULL", extra->flinfo.fn_oid); |
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return result; |
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} |
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/*
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* Set up a shim function to allow use of an old-style btree comparison |
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* function as if it were a sort support comparator. |
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*/ |
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void |
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PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup) |
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{ |
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SortShimExtra *extra; |
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extra = (SortShimExtra *) MemoryContextAlloc(ssup->ssup_cxt, |
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sizeof(SortShimExtra)); |
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/* Lookup the comparison function */ |
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fmgr_info_cxt(cmpFunc, &extra->flinfo, ssup->ssup_cxt); |
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/* We can initialize the callinfo just once and re-use it */ |
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InitFunctionCallInfoData(extra->fcinfo, &extra->flinfo, 2, |
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ssup->ssup_collation, NULL, NULL); |
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extra->fcinfo.argnull[0] = false; |
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extra->fcinfo.argnull[1] = false; |
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ssup->ssup_extra = extra; |
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ssup->comparator = comparison_shim; |
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} |
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/*
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* Fill in SortSupport given an ordering operator (btree "<" or ">" operator). |
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* |
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* Caller must previously have zeroed the SortSupportData structure and then |
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* filled in ssup_cxt, ssup_collation, and ssup_nulls_first. This will fill |
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* in ssup_reverse as well as the comparator function pointer. |
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*/ |
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void |
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PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup) |
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{ |
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Oid sortFunction; |
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bool issupport; |
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if (!get_sort_function_for_ordering_op(orderingOp, |
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&sortFunction, |
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&issupport, |
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&ssup->ssup_reverse)) |
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elog(ERROR, "operator %u is not a valid ordering operator", |
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orderingOp); |
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if (issupport) |
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{ |
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/* The sort support function should provide a comparator */ |
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OidFunctionCall1(sortFunction, PointerGetDatum(ssup)); |
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Assert(ssup->comparator != NULL); |
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} |
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else |
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{ |
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/* We'll use a shim to call the old-style btree comparator */ |
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PrepareSortSupportComparisonShim(sortFunction, ssup); |
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} |
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} |
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@ -0,0 +1,156 @@ |
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/*-------------------------------------------------------------------------
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* |
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* sortsupport.h |
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* Framework for accelerated sorting. |
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* |
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* Traditionally, PostgreSQL has implemented sorting by repeatedly invoking |
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* an SQL-callable comparison function "cmp(x, y) returns int" on pairs of |
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* values to be compared, where the comparison function is the BTORDER_PROC |
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* pg_amproc support function of the appropriate btree index opclass. |
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* |
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* This file defines alternative APIs that allow sorting to be performed with |
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* reduced overhead. To support lower-overhead sorting, a btree opclass may |
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* provide a BTSORTSUPPORT_PROC pg_amproc entry, which must take a single |
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* argument of type internal and return void. The argument is actually a |
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* pointer to a SortSupportData struct, which is defined below. |
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* |
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* If provided, the BTSORTSUPPORT function will be called during sort setup, |
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* and it must initialize the provided struct with pointers to function(s) |
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* that can be called to perform sorting. This API is defined to allow |
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* multiple acceleration mechanisms to be supported, but no opclass is |
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* required to provide all of them. The BTSORTSUPPORT function should |
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* simply not set any function pointers for mechanisms it doesn't support. |
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* (However, all opclasses that provide BTSORTSUPPORT are required to provide |
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* the comparator function.) |
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* |
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* All sort support functions will be passed the address of the |
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* SortSupportData struct when called, so they can use it to store |
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* additional private data as needed. In particular, for collation-aware |
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* datatypes, the ssup_collation field is set before calling BTSORTSUPPORT |
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* and is available to all support functions. Additional opclass-dependent |
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* data can be stored using the ssup_extra field. Any such data |
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* should be allocated in the ssup_cxt memory context. |
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* |
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* Note: since pg_amproc functions are indexed by (lefttype, righttype) |
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* it is possible to associate a BTSORTSUPPORT function with a cross-type |
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* comparison. This could sensibly be used to provide a fast comparator |
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* function for such cases, but probably not any other acceleration method. |
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* |
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* |
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* Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* src/include/utils/sortsupport.h |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#ifndef SORTSUPPORT_H |
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#define SORTSUPPORT_H |
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#include "access/attnum.h" |
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typedef struct SortSupportData *SortSupport; |
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typedef struct SortSupportData |
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{ |
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/*
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* These fields are initialized before calling the BTSORTSUPPORT function |
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* and should not be changed later. |
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*/ |
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MemoryContext ssup_cxt; /* Context containing sort info */ |
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Oid ssup_collation; /* Collation to use, or InvalidOid */ |
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/*
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* Additional sorting parameters; but unlike ssup_collation, these can |
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* be changed after BTSORTSUPPORT is called, so don't use them in |
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* selecting sort support functions. |
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*/ |
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bool ssup_reverse; /* descending-order sort? */ |
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bool ssup_nulls_first; /* sort nulls first? */ |
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/*
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* These fields are workspace for callers, and should not be touched by |
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* opclass-specific functions. |
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*/ |
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AttrNumber ssup_attno; /* column number to sort */ |
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/*
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* ssup_extra is zeroed before calling the BTSORTSUPPORT function, and |
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* is not touched subsequently by callers. |
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*/ |
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void *ssup_extra; /* Workspace for opclass functions */ |
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/*
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* Function pointers are zeroed before calling the BTSORTSUPPORT function, |
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* and must be set by it for any acceleration methods it wants to supply. |
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* The comparator pointer must be set, others are optional. |
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*/ |
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/*
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* Comparator function has the same API as the traditional btree |
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* comparison function, ie, return <0, 0, or >0 according as x is less |
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* than, equal to, or greater than y. Note that x and y are guaranteed |
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* not null, and there is no way to return null either. Do not return |
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* INT_MIN, as callers are allowed to negate the result before using it. |
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*/ |
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int (*comparator) (Datum x, Datum y, SortSupport ssup); |
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/*
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* Additional sort-acceleration functions might be added here later. |
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*/ |
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} SortSupportData; |
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/* ApplySortComparator should be inlined if possible */ |
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#ifdef USE_INLINE |
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/*
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* Apply a sort comparator function and return a 3-way comparison result. |
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* This takes care of handling reverse-sort and NULLs-ordering properly. |
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*/ |
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static inline int |
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ApplySortComparator(Datum datum1, bool isNull1, |
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Datum datum2, bool isNull2, |
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SortSupport ssup) |
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{ |
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int compare; |
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if (isNull1) |
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{ |
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if (isNull2) |
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compare = 0; /* NULL "=" NULL */ |
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else if (ssup->ssup_nulls_first) |
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compare = -1; /* NULL "<" NOT_NULL */ |
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else |
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compare = 1; /* NULL ">" NOT_NULL */ |
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} |
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else if (isNull2) |
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{ |
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if (ssup->ssup_nulls_first) |
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compare = 1; /* NOT_NULL ">" NULL */ |
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else |
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compare = -1; /* NOT_NULL "<" NULL */ |
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} |
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else |
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{ |
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compare = (*ssup->comparator) (datum1, datum2, ssup); |
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if (ssup->ssup_reverse) |
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compare = -compare; |
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} |
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return compare; |
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} |
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#else |
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extern int ApplySortComparator(Datum datum1, bool isNull1, |
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Datum datum2, bool isNull2, |
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SortSupport ssup); |
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#endif /* USE_INLINE */ |
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/* Other functions in utils/sort/sortsupport.c */ |
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extern void PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup); |
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extern void PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup); |
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#endif /* SORTSUPPORT_H */ |
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